The absolute threshold of a modality is examined by repeatedly presenting a series of fixed stimuli in random order and asking the subject to report if they detect it or not. The threshold is determined as the value that was detected 50% of the time.

A differential threshold is explored by repeatedly presenting a series of fixed stimuli in random order and asking the observer to report on the size relative to a comparison stimulus. The threshold is determined to be the point at which the subject notes a just noticeable difference from the comparison stimulus on 50% of the trials